Production of salt cake and hydrogen chloride



July 6, 1937. w. c. BAILEY PRODUCTION OF SALT CAKE AND HYDROGEN CHLORIDE m m zo-...Omm mmwa-m M W N 25E :son

INVENTOR.y

WALDO C. BAILEY ,l

BY M ATTO EY.

Patented July 6, 1937 UNITED; s'rATs PATENT OFFICE Y l y 72,086,206 Y f PRODUCTION oF SALT CAKE AND HYDRon GEN CHLORIDE l Waldo Conkling Bailey, Shaker- Heights, Ohio, assignorby mesne assignments,-to E. I. du

PontV de Nemours Y,&. Company, Wilmington, Del.,V a corporation of Delaware Applix'aaftionlifebruaryy 21, 1936, Serial No. 64,997

in my salt cake furnace being a single gas space above said pot and hearth into which the-hydrogen chloride gas 'is`"delivered, indirect heating of the reaction mass both in the pot and on theY hearth, with a single combustion gas system for circulation around the pot and said hearth, the

latter -formingrthereby a'muiile, the circulation of the heating gas proceeding from above'the pot, abovethe Inutile, then below the muiile and below the pot to thev stack; control of the heating by admission of the combustion air at various points along the course Vof said combustion Vgas and use ofv silicon carbide refractories inthe construction of the separation arches between the Vgas space containing the hydrogen chloride and the cornbustion zone containing the Vhot combustion gases. Y l

The attached Figure 1 shows a side elevation of a salt cake furnace built Vaccording to my invention; Figs. 2 and 3 are elevations along the 'lines A-A and B-B of Fig. 1.

It has been customary in pot-hearth type salt cake furnaces to separately heat the pot and the hearth, the pot being heated from beneath and the charge in the hearth being in direct contact with the re gases. This made it advisable to separately recover and absorb the hydrogen chloride gases formed, the gases from the pot being highly concentrated and adapted to make strong hydrochloric acid; the hydrogen chloride evolved on the hearth was diluted with combustion gases and dilute hydrochloric acid could only be directly obtained from hearth gases.

In other pot-hearth type furnaces, the hearth has been heated indirectly but here again, with separate heating provided for both, the gases evolved were separately recovered and absorbed.

It has, however, in all these installations been the absolute practice to heat the po-t from below.

These manners of operating salt cake furnaces of the non-mechanical type result in large repair costs, particularly frequent replacements of the cast iron pots are required.

According to my invention I apply the maximum heat above the pot and hearth through a silicon carbide refractory arch, and the bottom of the hearth and pot is then only heated by the uegases after combustion. Additional protec tion can then be had for the cast iron pot by shielding its `bottom from the fire gases by la row of silicon carbide refractory tile. I

In the appended drawing, I is a cast iron pot set in a fire brick structure. The lip of the pot is ush with the hearth2. The two are covered by a single siliconrefractory arch 3, formingvmuiile il; an opening with sleeve .5 in the arch above the pot servesv as a charging hole for the' salt and acid; openings 6 inv the side walls of the mule provide'for outlets of the HC1 gas formedfwhich, from A`Vthese holes, is' led to an absorption system, not shown. Doors 'l at both ends of the mufliepermit the introduction of 1 raking and spreading toolsr needed to transfer the soup out" ofthe pot, to spread it over the' .3,"and` through varying thev admission of airV throughL theseinlets the combustion of the` vela-Y tile fuel is 'controlled so'that the"requiredtem' peratures are obtained in the pot I, and on the hearth 2. The combustion gases are led do-wnwards at the discharge end of the mule through down flues I2 into the return flues I3, which pass beneath the hearth 2 and pot I, and are led to a stack, not shown. A row of silicon carbide refractory tile formsI a shield I4 under pot lv so that the still hot combustion gases. do not come in direct contact with the metal of pot I, whereby its life is greatly prolonged.

In operating this furnace, the charge of salt is dumped into the pot through charging hole 5 and then hot sulfuric acid (about 62 B.) is slowly run in through the samehole. The acid addition is regulated by the operator so that the gas evolution is fairly uniform and the charge does not foam over. When the charge is about reacted, and has become a semi-fluid mush or soup, it is dragged upon the hearthof the muflle by means of the tools introduced through doors 1; there it is spread out and is periodically rabbled and plowed. After the pot charge has been put upon the hearth, the Ynext charge is put into the pot, so that two charges, one in the pot and one on the hearth, are in process at the the pot and applying all heat through the arch same time. Temperatures are maintained by controlling the combustion in flue 9 so that the pot and mule reactions take about the same time for completion. The salt cake formed on the hearth is raked out just before the pot charge is ready for transfer to the hearth.

The HCl gas from both the pot and hearth is withdrawn through common ports in the side Wall of the mufile.

The use of silicon carbide refractories in the arch over the pot makes it possible to put all or almost all of the heat required by the pot charge in from above, thus making it possible to run at high burdens without maintaining a high temperature under the pot and thereby causing thermal strains which result in pot failures.

The high pot repairs which would obtain if high burdens were run with heat input from below formerly limited the capacity of such a system, whereas the capacity of the pot is greatly increased by this novel heating from above. In changing over a system in which the pot was heated from below and thecharge in the hearth heated directly by combustion gases, to a system according to the present invention, withoutv changing the dimensions of the pot or hearth, the capacity of the system has been increased 50%.

Further advantage resulting from this overhead heating is that when the pot is made of `metal there is less attack ofthe acid and the resulting salt cake contains less iron contamination as in the case of iron pots heated entirely from below.

By completely eliminating the under-firing of 1. In a salt cake furnace for the production of sodium sulfate and hydrogen chloride gas, the combination of a pot adapted to receive and heat sulfuric acid and common salt, a hearth adapted for further heating the reacting mixture of acid and salt obtained in said pot, a muflle within which a single gas space extends over the reaction mixture contained in bothv said pot and hearth, adapted to receive the gaseous hydrogen chloride produced in said pot and on said hearth and to lead said hydrogen chloride to an'absorption system, a combustion space surrounding both said pot and hearth, separated from said gas space, and adapted to burn a volatile fuel, means to admit the volatile fuel into the combustion space above said pot and to circulate the combustion gases on top of said muiile, returning them under the muffle, air ports in said combustion space throughout its length above said muiile adapted to regulate the admission of air into said combustion space and thereby regulate the combustion of said volatile fuel and the temperature in said gas space, and silicon carbide refractories forming the separating partition between said gas space and said combustion space.

2. The salt cake furnace of claim l in which the hot combustion gases are passed under said pot and a silicon carbide refractory is interposed between the bottom of said pot and the hot combustion gases.

3. In a salt cake furnace of the type comprising a pot and a hearth provided with a single gas space for collecting hydrogen chloride, an inlet above the pot for admitting a heating fluid and thereby rst applying heat to the pot roof,

a passage above the hearth for next conveying the heating fluid from'above the pot along thehearth roof, a passage below the hearth for next conveying the heating fluid from above the hearth along the hearth iloor, and a passage associated with the pot for finally conveying the heating fluid from below the hearth and directing it towards the lower portion of the pot and in indirect heat exchange relation thereto.

4. In a salt 4cake furnace of the type comprising a pot and a hearth provided with a single gas space for collecting hydrogen chloride, a fuel inlet above the pot, means for admitting air whereby a major portion of the heating value of the fuel is developed and applied at the pot roof, and means for applying successively lesser portions of heat to the top of the hearth, the floor of the hearth, and the bottom of the pot.

WALDO CONKLING BAILEY. 

